The invention relates to a window for a hot chamber, which is sealed off from its surroundings. The window comprises a multi-pane module having at least two transparent panes held apart by peripheral spacers, which panes are interconnected with the spacers in gas-tight fashion.
Hot chambers that are sealed off from their surroundings and have high temperatures during operation typically have a window to allow viewing of the hot chamber from the outside. Depending on the application, the window can be permanently installed in the walls bordering the hot chamber. In the case of a typical application, however, the window can also be integrated in a door of a wall bordering the hot chamber. Typical examples of this are oven doors, such as doors of ovens used for baking, in particular those with pyrolytic self-cleaning features, or microwave ovens.
Windows can also be provided in fireproof doors that seal off a chamber that becomes a hot chamber if fire breaks out.
Windows for the aforementioned purposes typically comprise multi-pane modules having at least two glass panes held apart by spacers in a connecting frame.
A window of this type for an oven door is presented, for example, in DE 44 07 084 A1 (=EP 0731 318 B 1). The known window has a window assembly having two glass panes arranged in a connecting frame, which forms a glass pane composite. This window assembly is mounted in the door with an empty layer of air separating it from a front glass pane and forms a multi-pane module with the front glass pane. The glass pane compositexe2x80x94which itself is vapor-tightxe2x80x94is formed by a peripheral seal, in particular a glass fiber seal, that is effective even under the influence of heat, in order to prevent water vapor or steam from the oven muffle from entering the space between the two glass panes of the window assembly and soiling the window. In order to keep such water vapor and steam away from the front pane of the window as well, a peripheral flow barrier is also provided in the empty space between the front pane and the window assembly. This known construction has the disadvantage in particular that pressure builds up because of an increase in temperature throughout the hermetically sealed, empty space between the glass panes of the window assembly, which significantly shortens the service life of the multi-pane module.
In order to compensate for this pressure increase, the known construction according to DE 43 33 033 C1 (EP 0 646 753 B1) provides a spacer developed as a compressible silicone tube. The tube volume makes pressure compensation possible when temperature changes occur. The panes separated by the spacer are interconnected with each other, together with the spacer, in hermetically-sealed fashion by means of a temperature-resistant bonding agent, in particular a silicone bonding agent.
The glass pane exposed to the internal chamber temperature of the apparatus is typically composed of THERMAX 5000(copyright), a prestressed soda-lime float glass coated in heat-reflecting fashion, and the glass pane exposed to the ambient temperature and, if applicable, a further internal intermediate pane, are composed of DURAX(copyright), a prestressed soda-lime float glass.
As a result of the compressible spacer, the distance between the glass panes depends on the temperature, because of which special structural requirements are placed on the design of the mechanical holders of the glass panes, the interconnecting frame. Moreover, the spacer is continuously subjected to deformations, which does not have a favorable effect in terms of material fatigue.
A window for fire-retardant glass having a multi-pane module is described in DE 36 37 064 C2 in which the panes are held apart by a sealing mass, on the one hand, and, on the other, are interconnected in sealed fashion. This multi-pane module has a very expensive pressure compensation system with valves that open in case of fire and release the gas pressure building up as a result of increasing temperature before it causes the panes to burst. Such a multi-pane module can also be provided with a metallic frame at considerable production-engineering expense. DE 39 15 687 C2 teaches an edge enclosure composed of a flexible, gas-permeable band for this module.
An evacuated insulating glass composed of two panes having, e.g., cylindrical, spacers between them distributed according to a certain pattern is also known. The edges of the glass panes are hermetically sealed using either glass solder or metal solder in order to prevent air from entering. The distance between the panes is approximately 100 xcexcm.
This multi-pane module has a number of disadvantages. For instance, thermally and/or chemically prestressed glass cannot be used, since the soldering temperatures are typically higher than the relaxation temperature of the prestressed glass. Moreover, the flatness of thermally prestressed glasses has deviations that make it impossible to realize the extremely close separations. Destressed glass must either have a thickness of at minimum 6 mm in order to withstand the vacuum, as a result of which the module becomes extremely heavy, or the spacer pattern must be configured so that it is sealed very tightly, which makes it difficult to look through. When special solders for low soldering temperatures are used, the seal is at risk of breaking during use. Additionally, it must be assumed that the panes will bend under the temperature load and then touch each other; prevention of thermal conductance would no longer be ensured.
It is an object of the present invention to provide a window of the above-described kind for a hot chamber sealed off from the surroundings, designed as a multi-pane module having at least two transparent panes held apart by peripheral spacers, which are interconnected in gas-tight fashion with the spacers, so that, despite the gas-tight connection between the spacers and the panes, pressure compensation can be obtained between the space between the panes and the surroundings using simple means without allowing the windows to become soiled.
This object is attained according to the invention by providing at least one opening in the spacers that is closed with a permeable filter that allows gasses to penetrate for purposes of pressure compensation, but prevents steam and water vapor from entering.
If increased pressure resulting from a temperature increase therefore develops in the space between the panes, air can escape from the interior space via the filter. When the space between the panes cools down again, filtered ambient air flows back into the intermediate space. Any steam or water vapor is thereby deposited in the filter and is filtered out. According to a preferred embodiment of the invention, the filter is advantageously replaceable. The filter is preferably a filter pad for this purpose.
According to another preferred embodiment, the panes are preferably made out of a glass having high thermal resistance, e.g., a thermally and/or chemically prestressed borosilicate glass.
According to an alternative preferred embodiment, the panes are composed of a glass ceramic that is highly temperature-resistant.
According to an advantageous embodiment of the invention, the spacers are preferably composed of stainless steel, aluminum, or a sufficiently temperature-resistant plastic.
To obtain an interconnected assembly, the spacers are bonded with the panes, according to an embodiment of the invention, using a temperature-resistant bonding agent, preferably a silicone bonding agent.
In order to obtain a further temperature reduction in the pane facing away from the hot chamber, the window according to the invention is advantageously designed so that at least one of the panes is provided with a thermal radiation-reflecting layer on at least one side.